A lithographic apparatus is a machine that applies a desired pattern onto a substrate, usually onto a target portion of the substrate. A lithographic apparatus can be used, for example, in the manufacture of integrated circuits (ICs). In that circumstance, a patterning device, which is alternatively referred to as a mask or a reticle, may be used to generate a circuit pattern to be formed on an individual layer of the IC. This pattern can be transferred onto a target portion (e.g. including part of, one, or several dies) on a substrate (e.g. a silicon wafer). Transfer of the pattern is typically via imaging onto a layer of radiation-sensitive material (resist) provided on the substrate. In general, a single substrate will contain a network of adjacent target portions that are successively patterned. Conventional lithographic apparatus include so-called steppers, in which each target portion is irradiated by exposing an entire pattern onto the target portion at once, and so-called scanners, in which each target portion is irradiated by scanning the pattern through a radiation beam in a given direction (the “scanning”-direction) while synchronously scanning the substrate parallel or anti-parallel to this direction. It is also possible to transfer the pattern from the patterning device to the substrate by imprinting the pattern onto the substrate.
In conventional lithographic apparatus of the above-mentioned type an exchangeable object handling apparatus may be used for the exchange of exchangeable objects between a stationary exchangeable object station and an exchangeable object support on which the exchangeable object during an operational phase is supported. Such exchangeable object may be a substrate which is exchanged between a substrate station and a substrate support, such as a substrate table on which the substrate is supported during the transfer of a pattern on the substrate. The exchangeable object may also be a patterning device which is exchanged between a patterning device loading station and a patterning device support on which during an operational phase the patterning device is supported.
Production capacity of a lithographic apparatus is, in part, affected by the exchange time needed to take away, after illumination, a substrate, which is located on the substrate support, and to place another substrate on the substrate support for a subsequent illumination. In order to increase the capacity of the lithographic apparatus it is desirable to decrease this exchange time.
In order to keep the exchange time small, the substrate handling apparatus of a conventional lithographic apparatus includes a robot with a double end-effector, i.e. robot capable of holding at the same time two substrates in two different holding positions. The double end-effector can be rotated around its vertical axis so that one of the two holding positions can be turned to a position wherein the robot can exchange a substrate with the substrate support. In another position, usually when the double end-effector is rotated over 180 degrees, a substrate in the other of the two holding positions can be exchanged with the substrate support.
When a first substrate held in the substrate support is to be exchanged by a second substrate which is placed in a loading station, the second substrate can during the transfer of a pattern on the first substrate, be placed in one of the holding positions of the robot. When the transfer is finished, the first substrate is taken from the substrate support in the other one of the holding positions of the robot. After that the double end-effector is rotated the second substrate is placed on the substrate support. Subsequently a pattern can be transferred on that second substrate. During this pattern transfer the robot can place the first substrate in the loading station. As the robot can hold two substrates at the same time the robot with double end-effector makes a relative quick exchange of the first and second substrate possible.
However, in conventional substrate handling apparatus, the robot with double end-effector is a relative expensive part of the lithographic apparatus, also due to the space needed to make the movement of the robot and in particular the rotating movement of the double end-effector in the lithographic apparatus in the proximity of the substrate support possible.
Alternatively, two robots which each can exchange an exchangeable object with a stationary station and the support may be provided. However, this solution may be expensive and may require a lot of footprint.